Circuit arrangement for supplying a control electronics system in electric machines

ABSTRACT

A circuit configuration for supplying the control electronics in an electrical machine is specified, which includes a passive transformer circuit, which is powered by a phase current IP of the electrical machine and which generates an auxiliary voltage VA that is used for supplying the output stage of the electrical machine if no battery is present or if the battery is defective or discharged.

FIELD OF THE INVENTION

The present invention is based on a circuit configuration for supplyingthe control electronics of electrical machines and relates in particularto supply circuits for starter-generators in motor vehicles which canalso be operated without battery.

BACKGROUND INFORMATION

Usually, two electrical machines are used in motor vehicles, agenerator, which is driven by the engine of the motor vehicle and whichgenerates electrical energy for supplying the electrical-systemconsumers and for charging the battery, and a starter, which works as abattery-powered electrical motor and which, in the event of a startingoperation, brings the engine of the motor vehicle up to a requiredminimum rotational speed. Also known, however, are systems featuring asingle electrical machine, which takes the form of a starter-generatorand which accomplishes both the starting of the engine as well as thegeneration of the electrical energy.

Such starter-generators are, for example, flywheel starter-generators orcrankshaft starter-generators directly connected to the crankshaft ofthe engine. The starter-generators used in this context are three-phasemachines, which can be connected to the vehicle battery via a powerelectronics that includes a controlled rectifier bridge, in particular apulse-controlled a.c. converter with a pulse-controlled inverter bridge.The pulse-controlled inverters are controlled using a controlelectronics.

If the electrical machine, for example, is a permanent-field synchronousmachine, then the rotating machine will generate a voltage regardless ofwhether the electronics is activated or not. In the case of sufficientlyhigh rotational speeds of the synchronous machines this can lead to anexceeding of the permitted voltage and there is the danger of destroyingthe electronics of the starter-generator as well as the electricalsystem electronics.

A vehicle electrical system having a starter-generator as well as amethod for the automatic control of such a starter-generator, which canbe connected to the vehicle battery via a pulse-controlled inverterbridge, is described in German Published Patent Application No. 197 33212 for example. In this known system, the pulse-controlled inverterelements of the converter bridge are suitably controlled with the aid ofa control electronics in such a way that an optimal generator control isachieved in generator operation and hence a maximum of electrical poweris generated. At the same time, a suitable control of thepulse-controlled inverter elements ensures that in a starting operationthe electrical machine can draw electrical power from the battery andthereby working as a motor can accelerate the vehicle engine to therotational speed required for starting.

Since it is possible that the vehicle battery is destroyed during theoperation of the vehicle or that the battery is largely drained due tounfavorable circumstances, there is the danger that in the resultingso-called batteryless operation, the electronics of the electricalmachine is no longer supplied. In this case, when the machine isshort-circuited and rotating, there exists no intermediate circuitvoltage which could supply the control electronics. Hence there is thedanger that, if the control electronics is not supplied, theshort-circuiting of the machine cannot be maintained. The consequencewould be an uncontrolled rise of the voltage. This could lead todestruction in the electronics of the electrical machine or of thestarter-generator and in the vehicle electrical system itself.

SUMMARY OF THE INVENTION

An objective of the present invention, therefore, is to ensure thesupply of the electronics of an electrical machine, particularly of astarter-generator, in the event of an operation without battery and witha short-circuited, rotating machine.

The circuit configuration of the present invention for supplying thecontrol electronics of electrical machines, particularly instarter-generators, has the advantage that the voltage supply for thecontrol electronics is ensured also in operation without battery andwith a short-circuited, rotating machine. This advantage is achieved byusing a passive transformer circuit powered by the phase current of theelectrical machine. This passive transformer circuit additionally hasthe special advantages of a low circuit complexity and only requires fewcomponent parts.

Particularly advantageous is the fact that as a matter of principle noclosed-circuit current flows for supplying the circuit and that thecircuit can be switched off. These further advantages are achieved bythe measures indicated in the subordinate claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are depicted in thedrawing and will be explained in greater detail in the followingdescription. The individual figures show:

FIG. 1 shows an electrical machine having a controlled bridge withshort-circuited low-side switches.

FIG. 2 shows a circuit configuration according to the present inventionfor supplying the control electronics in electrical machines.

FIG. 3 shows an example of a transformer design.

DETAILED DESCRIPTION

FIG. 1 shows a rough schematic representation of a voltage supplycircuit for an electric machine 10, in which d.c. voltage is supplied toelectrical machine 10 via a switchable bridge 11. The switchable bridgehere includes three high-side switch elements 12, 13, 14 and threelow-side switch elements 15, 16, 17, for example field-effecttransistors (MOSFETs) or appropriate pulse-controlled inverter elementsetc. and carries on the side opposite to ground a voltage U of 42 voltsfor example. The electrical machine 10 is connected in the usual mannerto the controlled rectifier bridge. The windings of the electricalmachine 10 are not represented in FIG. 1.

The switch elements of the rectifier bridge are suitably controlled by acontrol electronics 18. The voltage for control electronics 18 issupplied in normal operation from battery 19, via suitable voltageconverters if necessary. In the short-circuit case represented in FIG.1, low-side switch elements 15, 16, 17 are controlled (short-circuited)in such a way that they form a conductive connection to ground. For sucha control to be possible, a voltage has to be applied at the gate of thelow-side switch, which, according to the invention, is formed, in caseof a missing battery, from the phase current of the electrical machine.This voltage is called auxiliary voltage VA and is fed to switchelements 15, 16, 17 in place of the control voltage VC normally suppliedby control electronics 18.

FIG. 2 shows a detailed circuit configuration for supplying the controlelectronics in electrical machines or for forming an auxiliary voltageVA, which features a transformer circuit 20 as an essential component.Electrical machine 10 includes three phase windings 22, 23, 24 and isconnected to an output stage 21 via this transformer circuit 20. Outputstage 21 corresponds, for example, to controlled bridge 11 in FIG. 1,although only the two transistors T1 and T2 for a phase winding of theelectrical machine are represented.

The connecting point between the two transistors T1 and T2, that is, thephase connection Ph, is connected via the transformer T to thecorresponding phase winding, for example phase winding 23 of electricalmachine 10. In addition to the electrically isolated transformer Thaving primary winding P and secondary winding S, transformer circuit 20also includes a diode D, a capacitor C and a transistor T3 as well as alinear regulator L.

In the case of a short circuit, low-side switches 15, 16, 17 accordingto FIG. 1 or transistor T2 according to FIG. 2 are controlled, i.e.supplied with voltage, in such a way that a voltage is applied at thegate of the respective transistor. The relevant transistor is then in aconductive state. A nearly sinusoidal current IP flows across theprimary side of transformer T. A corresponding a.c. voltage is therebyinduced in the secondary side of transformer T. This a.c. current isrectified via diode D and capacitor C. The rectified voltage is fed tolinear regulator L, which stabilizes the voltage and provides at itsoutput the stabilized auxiliary voltage VA.

With the aid of transistor T3, which is normally switched on(normally-on transistor), transformer circuit 20 can be switched offwhen it is not required, if certain suitable, specifiable conditionsobtain, with no closed-circuit current flowing as a result.

Transformer T may be designed, for example, as an annular core AC. Phasecurrent IP of the primary side is then conducted through the center holeof annular core AC. The windings W of secondary side S are wound aroundannular core AC. FIG. 3 shows a possible refinement of transformer T.

1. A circuit configuration for supplying electrical energy to controlelectronics for an electrical machine whose phase windings are connectedto an output stage having controlled switches, comprising: a transformercircuit arranged between the output stage and the electrical machine,the transformer circuit being fed a phase current of the electricalmachine, whereby an auxiliary voltage is produced from the phasecurrent, the auxiliary voltage being used under specifiable conditionsto supply low-side switches of the output stage; and a controllableswitch element according to which a secondary side of the transformerswitches on or off under specifiable conditions which include at leastone missing or defective or discharged battery; wherein the transformercircuit includes a transformer, a primary side of the transformer isconnected to a phase winding of the electrical machine.
 2. The circuitconfiguration as recited in claim 1, wherein: the controllable switchelement includes a normally-on transistor.
 3. The circuit configurationas recited in claim 1, further comprising: a linear regulator connecteddownstream of the transformer circuit, wherein the linear regulator isfed a rectified voltage of a secondary winding of the transformer. 4.The circuit configuration as recited in claim 1, further comprising: adiode and a capacitor allocated to a secondary winding of thetransformer.
 5. The circuit configuration as recited in claim 1,wherein: the transformer includes an annular core, the phase current isconducted through a center hole, and windings of a secondary side of thetransformer are wound around the annular core.
 6. The circuitconfiguration as recited in claim 1, wherein the electrical machineincludes a starter-generator.